Zinc electroplating baths and process

ABSTRACT

A ZINC ELECTROPLATING BATH HAS A PH BETWEEN 3.5 AND 7.5 AND; IN ADITION, TO THE USUAL ZINC SALTS, CONDUCTING SALTS, BUFFERING SALTS, COMPLEX FORMING SALTS; INCLUDES (A) A BRIGHTENING AGENT OF THE TYPE PRODUCED BY THE REACTION OF ACETYLENIC ALCOHOLS WITH AROMATIC ALDEHYDES OR AROMATIC KETONES, (B) A WETTING AGENT OF THE TYPE PRODUCED BY CONDENSATION OF ETHYLENE OXIDE, (C) ABOUT 0.1-20 GRAMS/LITER OF A MONOCARBOXYLIC AROMATIC ACID (OR SALT THEREOF) HAVING THE CARBOXYL GROUP BONDED DIRECTLY TO THE AROMATIC NUCLEUS, AND (D) ABOUT 0.05-5 GRAMS/LITER OF AN AROMATIC ALDEHYDE OR AROMATIC KETONE.

United States Patent 3,778,359 ZINC ELECTROPLATING BATHS AND PROCESS Francine Popescu, nee Micsunescu, 32 Rue Etienne Solet, 94 Saint Maur, Val-de-Marne, France No Drawing. Continuation-impart of application Ser. No. 105,119, Jan. 8, 1971. This application Mar. 8, 1972, Ser. No. 232,916

Int. Cl. C23b /12, 5/46 US. Cl. 204-55 R 13 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of my copending patent application Ser. No. 105,119, filed J an. 8, 1971, in which I describe a process for obtaining brightening agents for electroplating baths, in particular zinc electroplating baths, in which one or several aldehydes or aromatic ketones are reacted under the influence of heat with one or several acetylenic alcohols in the presence of hydrochloric acid as catalyst.

This reaction mainly provides acetals and ketals of aromatic aldehydes and ketones with acetylenic alcohols which can be used as brightening agents in acid or neutral zinc electroplating baths of pH of about 3.57.5. The acetals and ketals thus prepared have the general formula:

where R is a member selected from the group consisting of aryl radicals; oxygen-containing heterocyclic radicals; and alkyl, hydroxyl, and alkoxy substituted aryl and oxygen-containing heterocyclic radicals; wherein R is a member selected fromthe group consisting of hydrogen, alkyl radicals, hydroxyalkyl, and aryl radicals; and where R and R which may be the same or diiferent, are radicals derived from said acetylenic alcohol.

The products thus defined are used in zinc electroplating baths in conjunction with non-anionic and anionic wetting agents derived from ethylene oxide and which serve as brightening agent carriers.

The object of the present invention is to improve the previously mentioned known electroplating baths. I have now found that plating from zinc baths containing such acetals or ketals yields brighter deposits with the addition of certain aromatic aldehyde or aromatic ketones.

The combination of such aldehyde or ketone with the above described acetal or ketal for the purpose of zinc electroplating results in the reduction of the quantity of the acetal brightening agent required and in the obtaining O-Ra 3,778,359 Patented Dec. 11, 1973 of zinc coating of lighter color. The concentration of free aromatic aldehydes or ketones combined with the acetal brightening agent, according to the present invention, may generally be between 0.05 gram/liter and 5 grams/liter in the zinc plating bath, but it is preferable to remain within the limits of 0.05 to 0.5 gram/liter. Further, the ratio of acetal or ketal to aldehyde or ketone is maintained between 3 and 10. A greater concentration of free aromatic aldehydes or ketones may unfavorably influence the quality of the zinc coatings, reducing their ductility and causing pits to appear.

Table I shows by way of non-limiting examples some aromatic aldehydes and ketones which can be used, according to the present invention, in combination with the above described acetals or ketals.

TABLE I Benzaldehyde C H -CHO Methylbenzaldehyde CH C H CHO Cuminic aldehyde p-(CH) CHC H CHO Cinnamic aldehyde C H CH=CHCHO o-hydroxybenzaldehyde C H ,(OH)CHO p-methoxybenzaldehyde C H (CH )CHO These, generally, are carbonyl compounds of the general formula:

where R; is a member selected from the group consisting of aryl radicals; oxygen-containing heterocyclic radicals; and alkyl, hydroxyl, and alkoxy substituted aryl and oxygen-containing heterocyclic radicals; and where R, is a member selected from the group consisting of hydrogen, alkyl radicals, hydroxyalkyl, and aryl radicals.

I have found further that; although acid or neutral zinc electroplating baths which contain the brightening agents described in my above identified copending patent application give coatings of bright appearance and of high quality; this quality can be improved by adding to such brightening agents, at least one monocarboxylic aromatic acid (or salt thereof), having a carboxyl group directly bonded to the aromatic nucleus. The latter additive increases the penetrating power of the deposits and gives a lighter color in the zones where the current density is low.

The monocarboxylic aromatic acids used according to the present invention have the general formula:

(PEPE-4) )nM where R is a member selected from the group consisting of aryl radicals; oxygen-containing heterocyclic radicals; nitrogen-containing heterocyclic radicals; and halogen, alkyl, hydroxy, alkoxy substituted aryl radicals, oxygencontaining heterocyclic radicals and nitrogen-containing heterocyclic radicals; where M is a member selected from the group consisting of hydrogen, zinc, the ammonium radical, and alkali metals; and where n is an integer from 1 to 2.

Table II shows by way of non-limiting examples some aromatic acids which can be used in the process according to the present invention.

TABLE II Benzoic acid C H COOH o-, m-, and p-toluic acids CH C H COOH m-, and p-hydroxybenzoic acids HOC H -COOH o-, and p-chlorobenzoic acids CLC H COOH Anisic acid CH OC H COOH Vanillic acid CH O(OH)C H COOH Piperonylic acid CH O C H COOH Beta-resorcilic acid (OH) C H COOH Furoic acid C H OCOOH Nicotinic acid C H NCOOH Picolinic acid C H ,COOH

To best utilize the method according to the present invention; that is, to electroplate zinc on a basis metal; one adds to an acid or neutral zinc plating bath, one or several brightening agent carriers chosen from nonanionic and anionic wetting agents derived from ethylene oxide in an amount of 1-50 grams/liter; about 0.05-5 grams/liter of at least one brightening agent selected from the reaction product of an acetylenic alcohol with an aromatic aldehyde or aromatic ketone; about 0.1-20 grams/liter of one or several acids exemplified in Table II, or their sodium, potassium, zinc or ammonium salts; and about 0.05-1 grams/liter of at least one aromatic aldehyde or aromatic ketone exemplified in Table I.

The zinc coatings obtained by the composition and method of the present invention give an increased brightness and leveling, a still further improved penetrating power which can exceed that of the usual zinc plating baths containing cyanides, and a uniform degree of brightness and a light color over a very wide range of cathodic current densities.

The following examples illustrate the composition of zinc electroplating baths according to the present invention:

pH4.5-5.0; temperature: 2030 C.: 24 a./dm.

The zinc coatings obtained in this bath, with cathodic stirring, are very bright, uniform and level.

current density:

EXAMPLE II Grams/liter Zinc chloride 90 Ammonium chloride 250 Condensation product of benzaldehyde with 2- butyne-l, 4-diol 0.5 Anisic acid (or its alkali salts) 0.8 Non-ionic wetting agent, alkyphenoxy-poly '(ethyleneoxy) ethanol 10 Under the same conditions as in Example I, very bright zinc coatings of a light color and having a remarkable penetrating power are obtained.

4 EXAMPLE III Grams/liter Zinc chloride Ammonium chloride 230 Condensation product of benzaldehyde with 2- butyne-l, 4-diol 0.4 Benzaldehyde 0.1 p-Hydroxybenzoic acid 0.4 o-Toluic acid 0.2 Non-ionic wetting agent, alkylphenoxy-poly (ethyleneoxy) ethanol 10 Under the same conditions as in the preceding example, the same results are obtained.

It will be apparent to one skilled in the art to which the invention pertains that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. An aqueous, zinc-ion-containing zinc electroplating bath having a pH in the range of about 3.5-7.5 and comprising the combination of about 0.05-5 grams of a brightening agent having the formula:

wherein R is a member selected from the group consisting of phenyl, methyl phenyl, isopropyl phenyl, phenyl methyl, phenyl vinyl, methoxy phenyl, methylene dioxy phenyl, furyl, and hydroxy phenyl radicals; and R is a member selected from the group consisting of the methyl radical and hydrogen.

2. The bath according to claim 1 'wherein the concentration of said brightening agent and the concentration of said compound are in a ratio in the range of 3-10.

3. The bath according to claim 1 wherein said compound selected from the group of aldehydes and ketones is benzaldehyde.

4. The method of electroplating zinc on a basis metal which comprises the step of electroplating from a bath comprising the composition of claim 1.

5. An aqueous, zinc-ion-containing zinc electroplating bath having a pH in the range of about 3.5-7.5 and comprlsmg the combination of about 0.05-5 grams of a brightening agent having the formula:

R1 OR3 wherein R is selected from the group consisting of phenyl, methyl phenyl, isopropyl phenyl, phenyl methyl, phenyl vinyl, hydroxy phenyl, methoxy phenyl, methylene dioxy phenyl and furyl radicals;

R is selected from the group consisting of the methyl radical and hydrogen; and R and R which may be the same or different, are each selected from the group consisting of alkyne, methyl substituted alkyne, and hydroxy substituted alkyne radicals; and about 0.1-20 grams per liter of a compound selected from the group consisting of piperonylic acid; furoic acid, nicotinic acid; picolinic acid; an acid having the formula:

wherein R is selected from the group consisting of phenyl, methyl phenyl, hydroxy phenyl, chlorophenyl, methoxy phenyl, methoxy hydroxy phenyl radicals; and the zinc, ammonium, and alkali metal salts of said acids.

6. The bath according to claim 5 and comprising additionally about 0.5-5.0 gram per liter of a compound selected from the group of aldehydes and ketones having the formula:

pound selected from the group of aldehydes and ketones is benzaldehyde and said acid is benzoic acid.

8. The bath according to claim 6 wherein R is phenyl, R is hydrogen, R and R are butyne, said compound selected from the group of aldehydes and ketones is benzaldehyde, and said acid is a mixture of p-hydroxybenzoic acid and o-toluic acid.

9. The method of electroplating zinc on a basis metal which comprises the step of electroplating from a bath comprising the composition of claim 6.

10. The bath according to claim 5 wherein said acid is p-hydroxy benzoic acid.

11. The bath according to claim 5 wherein R is phenyl, R is hydrogen, R and R are butyne and said compound selected from the group of aldehydes and ketones is salicylaldehyde.

12. The bath according to claim 5 wherein R is phenyl, R is hydrogen, R and R are butyne, and said acid is anisic acid.

13. The method of electroplating zinc on a basis metal which comprises the step of electroplating from a bath comprising the composition of claim 5.

References Cited UNITED STATES PATENTS 3,296,104 1/1967 Eppensteiner 204- R 3,594,291 7/1971 Todt et a1 204-55 R GERALD L. KAPLAN, Primary Examiner 

